ABSTRACT:

We performed nano-indentation experiments on samples of Vaca Muerta shale, Argentina, taken from mature and immature outcrops, and reservoir cores, one from within the oil window. Elements were mapped at the indentation sites using energy-dispersive X-ray spectroscopy (EDX). The reduced elastic modulus, Er, hardness, H, and contact creep modulus, C were similar to those reported previously for source rocks from the US, except that the Vaca Muerta shale had a population of indentations with very low Er, H and C. High H was usually associated with pyrite, dolomite, calcite or quartz inclusions; the lowest values (H<0.1 GPa) were found at sites within the clay matrix in oil-window samples, possibly owing to the presence of organic material. We could not use EDX to verify this conjecture because the measurement sensitivity for C is low. Volumetric averaging of elastic and contact creep moduli from indentation tests gave values consistent with short-term triaxial tests on inch-scale shale samples, but these values were inconsistent with those measured in the lab over longer durations.

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